This invention relates to an optical component in the field of image generation systems such as are frequently used in aircraft and other simulators employing visual outputs. In simulators of the aircraft variety, for example, pilots observe a visual output which is a simulated view of the real world from their flight path.
The simulated view is typically produced from a small scale model of the real world with a closed circuit television system viewing the model world from the scale flight path through an optical probe that is passed or "flown" over the model.
An improved method for producing a simulated view is taught by my prior U.S. Pat. Nos. 3,580,660 and 3,639,034 both of which relate to the use of full color strip film to provide a two dimensional terrain model which contains no perspective but does employ aspect to add a three dimensional appearance to the simulated view. Perspective and aspect may be defined as follows:
1. Perspective is the phenomenon which causes rectangular objects to appear as trapezoidal objects. Stated another way, perspective is the phenomenon which causes lines which are parallel to appear to run to a vanishing point. When the observer's eyepoint changes in vertical, lateral or longitudinal translation or in any combination from the point of photography, then, of course, the perspective must also be changed.
2. Aspect is the phenomenon which identifies the viewing angle of objects. For example, the phenomenon of aspect makes a cube appear to have three sides when the viewing angle is looking toward one corner of the cube or makes a cube appear to have only one side when the viewing angle is normal to the side. Three dimensional aspect exists when three sides of a cube or other solid object can be seen.
The strip film image generator utilizes strip film without perspective but with the aspect as seen approximately 30.degree. down from the horizon. Perspective is regenerated optically. The reason for regenerating perspective continuously can be appreciated when one considers that the perspective view of any object at a distance varies as the observer translates his viewpoint with respect to said object. Hence, when the optical viewing system is translated over the projection of that portion of the strip film which represents the terrain surrounding the observer or vice versa, the true perspective from the observer's nadir to every point in his field of view will be regenerated. This perspective regeneration and optical relay of the observer's view to a television camera is accomplished by an optical system which is the subject matter of this invention.
The advantages of a full-color strip film image generation system have been enumerated and explained in my U.S. Pat. No. 3,639,034. It should be understood, however, that this invention is an improvement over the perspective regeneration system and film viewing optics of U.S. Pat. No. 3,639,034, and it also embraces a second strip film of weather effects in close proximity to the terrain strip film as in my earlier patent. This invention also contemplates the use of an overall image generation system and strip film rationale as disclosed in U.S. Pat. No. 3,639,034.
Because the present invention constitutes a true perspective viewing system providing views free from distortion, it is a very economical optical probe for viewing three dimensional models.
Prior probes used in simulation systems suffer many limitations such as the employment of very small entrance pupils to effect large depth of focus with the result that tremendous amounts of illumination must be poured onto the model. Even these small pupil probes do not fulfill the focus requirements. Another type of probe called the "tilt focus probe" using the Scheimpflug effect has been designed and used. Even this probe suffers from lack of illumination and, more importantly, from a lowered contrast rendition due to the number of glass elements that must be employed. Scheimpflug probes are also not able to focus very well on vertical prominences that protrude from the object plane such as tall buildings and mountains.
Prior optical probes have had limited fields of view (the widest field of view optical probe known has a 140.degree. circular field and was fabricated as a Scheimpflug probe). The present perspective regeneration system or probe overcomes the limited field restriction and supplies an instantaneous full hemisphere of view. The device maintains every point in the hemisphere in good focus from nadir to horizon around the full 360.degree. in azimuth while providing a high contrast rendition and is not limited in the focussing of large vertical objects. These features are achieved by the present invention at a closeness of approach of the probe to the screen or model of zero elevation, that is, the front optical element can actually be in contact with either screen or model.